Plug-in hybrid electric vehicles which combine an electric engine and an internal combustion engine are known in the art. During operation of a plug-in hybrid electric vehicle the internal combustion engine is used intermittently as the vehicle may run only on the electric engine. This causes the internal combustion engine to remain stationary for periods of time. During high performance manoeuvres such as overtaking another vehicle the internal combustion engine starts in order to provide extra power during the manoeuvre. As the internal combustion engine has not been used for some time the internal combustion engine is not properly lubricated when needed and is thus prone to excess wear during high performance manoeuvres. The same problem arises when an internal combustion engine is cold started as it takes time for the cold oil in the engine oil system to properly lubricate the engine.
There is thus a need for an improved engine oil system which addresses this problem.